If I have target locked(action bar) a ship and then it moves away from range 3 this turn. The following turn a new ship comes within range 3 (360 degree) of me can I target lock (action bar) this new ship and remove the old target lock from the previous targeted ship?

Yep.

You can Target Lock any one ship in range as long as: (1)You can perform a Target Lock action, (2)Have not performed a Target lock action this round, or (3)Some text on the enemy's build does not prevent the lock. No need for the first ship to fly out of range.